Ink jet printers are well known in the art. Generally, an ink jet printer includes an array of nozzles or orifices, a supply of ink, a network of channels connecting the array of nozzles with the ink supply, a plurality of ejection elements (typically either expanding vapor bubble elements or piezoelectric transducer elements) corresponding to the array of nozzles and suitable driver electronics for controlling the ejection elements. Typically, the array of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements which causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, overhead transparency, envelope or the like. Once they reach the print medium, the drops dry and collectively form a print image. Typically, the ejection elements are selectively activated or energized as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved.
Generally, the array of nozzles, supply of ink, plurality of ejection elements and driver electronics are packaged into an ink jet cartridge. In turn, the printer includes a carriage assembly for detachably mounting the ink jet cartridge thereto. In this manner, a fresh ink jet cartridge may be installed when the ink supply of the current ink cartridge has been consumed or the current ink cartridge has malfunctioned. However, in either case, the printer continues to operate with the result being that the user must recognize when the print quality degrades to an unacceptable level and install a fresh cartridge. Thus, it is generally intended for the cartridges to be disposable.
Recently, the postage meter industry and other envelope printing industries have begun to incorporate ink jet printers. A typical postage meter (one example of a postage printing system) applies evidence of postage, commonly referred to as a postal indicia, to an envelope or other mailpiece and accounts for the value of the postage dispensed. As is well known, postage meters include an ascending register, that stores a running total of all postage dispensed by the meter, and a descending register, that holds the remaining amount of postage credited to the meter and that is reduced by the amount of postage dispensed during a transaction. The postage meter generally also includes a control sum register which provides a check upon the descending and ascending registers. The control sum register has a running account of the total funds being added into the meter. The control sum register must always correspond with the summed readings of the ascending and descending registers. The control sum register is the total amount of postage ever put into the machine and it is alterable only when adding funds to the meter. In this manner, the dispensing of postal funds may be accurately tracked and recorded.
Since postal services accept postal indicia printed by postage printing systems as conclusive proof of payment of the amount of postage indicated, such devices are in effect machines for printing money. As a result, postal authorities that oversee operation of the postage printing systems impose high standards both on the print quality of postal indicia produced by such machines, and on the design of the machines themselves to assure that the appropriate amount is debited corresponding to the amount of postage indicated for each postal indicia.
With the incorporation of ink jet printing, postage printing devices now face the same problems associated with the use of ink jet cartridges as are found in general purpose ink jet printers. However, new problems also arise due to the inherent nature of printing an indicia of value. For example, if a general purpose ink jet printer runs out of ink while printing a document, then the user merely installs a new cartridge and reprints the document. On the other hand, if a postage printing device runs out of ink while printing a postal indicia, then the user loses money because the postal funds associated with that postal indicia cannot be recovered. As another example, if some of the ejection elements are not operating due to degradation of the ejection elements over time or some other malfunction condition, then the postal indicia will suffer from reduced print quality, even if adequate amounts of ink are present, resulting in a loss of optical character recognition (OCR) readability and loss of sufficient fluorescence necessary to be detected by a facer/canceller apparatus as a valid postal indicia. This will likely result in the mailpiece being returned to the sender by the postal authority. Again, the user loses money because the postal funds associated with that postal indicia cannot be recovered.
Therefore, there is a need for determining when a postage printing system is not in proper working condition. More particularly, there is a need for a postage printing system including an ink jet printer having an ink jet cartridge wherein the postage printing system performs a diagnostic routine to determine the operational status of the ink jet cartridge. In this manner, the user does not suffer a loss of funds by continuing to operate the postage printing system with a dysfunctional ink jet cartridge.